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Thread: physics brain teaser: fun with spaceships

  1. #31
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    Quote Originally Posted by BooBoo View Post
    “Why did the apple fall from the tree? Gravity.”

    Nope...!!!

    Newton formulated gravitational theory in 1665 or 1666 after watching an apple fall and asking why the apple fell straight down, rather than sideways or even upward. He showed that the force that makes the apple fall and that holds us on the ground is the same as the force that keeps the moon and planets in their orbits.

    He then laid it out in the Mathematica Principia, one of the foundation bedrocks of Physics and potentialy the most significant Physics Book every written.


    I sincerely hope you arent going to try and spout some bollox about him being wrong. Otherwise you'll join Captain kirk on my blocked list, his posts are generally too stupid to waste time reading.
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  2. #32
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    Quote Originally Posted by UKSmartypants View Post
    The gravitational force at any point ona body is calculated by the distance to the centre of the mass of whoms gravitational field you are currently influenced by. However in your example there are two components , one is the gravitational pull on you , which is slightly higher at your feet than your head, and demonstrated in an extreme gravitational field of a black hole, and the second component is the acelleration away from the mass by the rocket, which is a force pushing equally on all parts of the rocket. You are trying to conflate the two together in some weird sort of bastard gravitational mathematics which is nonsense..
    No, look at the OP question and my enumerated assumption of the only force affecting the ship being the acceleration due to the engines.

    Pretty tricky starting out talking about planetary gravity, and switching to acceleration *NOT* due to gravity. He specifies no directional gravitational force in the part with the question.
    Scientist, Evangelical Christian - reformed, father, entrepreneur, hunter, outdoorsman, motorcyclist, Constitutional Conservative.

  3. #33
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    Quote Originally Posted by Physics Hunter View Post
    No, look at the OP question and my enumerated assumption of the only force affecting the ship being the acceleration due to the engines.

    Pretty tricky starting out talking about planetary gravity, and switching to acceleration *NOT* due to gravity. He specifies no directional gravitational force in the part with the question.
    The question is about the people inside the ship.

    An observer outside the ship, sees a mass accelerating through space.

    But the people inside the ship, 'perceive' forces of various kinds. And since the ship is accelerating, they will in fact 'perceive' a curved universe. "As if" there were some gravity... (where?)

    And, the ship is losing mass (it's being converted into energy by the thrusters), but it's also gaining mass because of relativity.

    The people inside the ship "perceive" a force holding them to the back (bottom) floor, it "feels like" gravity.

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    Psst... the astute observer will just about realize, that I'm trying to go somewhere interesting with this.

    We "think" we live in Euclidean space and Minkowski spacetime, right?

    But how do we know for sure?

    How do we know we're not on the surface of a Dyson sphere, or accelerating through space in a rocket ship? Because if we look, we see a curved universe and it "feels like" gravity.

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    Quote Originally Posted by nonsqtr View Post
    The question is about the people inside the ship.

    An observer outside the ship, sees a mass accelerating through space.

    But the people inside the ship, 'perceive' forces of various kinds. And since the ship is accelerating, they will in fact 'perceive' a curved universe. "As if" there were some gravity... (where?)

    And, the ship is losing mass (it's being converted into energy by the thrusters), but it's also gaining mass because of relativity.

    The people inside the ship "perceive" a force holding them to the back (bottom) floor, it "feels like" gravity.
    The discussion between me and SmartAss ;-) was weather or not to assume that the ship was still in a planetary gravitational field, or not. I thought your question focused solely on the acceleration due to engines.

    Yes or No.
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    Quote Originally Posted by nonsqtr View Post
    Psst... the astute observer will just about realize, that I'm trying to go somewhere interesting with this.

    We "think" we live in Euclidean space and Minkowski spacetime, right?

    But how do we know for sure?

    How do we know we're not on the surface of a Dyson sphere, or accelerating through space in a rocket ship? Because if we look, we see a curved universe and it "feels like" gravity.
    If I read the word "manifold" you are going to hear me scream and run out of the thread!
    Scientist, Evangelical Christian - reformed, father, entrepreneur, hunter, outdoorsman, motorcyclist, Constitutional Conservative.

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    Quote Originally Posted by Physics Hunter View Post
    The discussion between me and SmartAss ;-) was weather or not to assume that the ship was still in a planetary gravitational field, or not. I thought your question focused solely on the acceleration due to engines.

    Yes or No.
    The general situation is something with mass being accelerated.

    The thing with mass presumably emits gravitons to begin with, and now it's undergoing additional acceleration.

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    Quote Originally Posted by UKSmartypants View Post
    its smaller at the tip, but the difference is minscule.

    The proof is the spaghettificiation that takes place as you approach a black hole. its precisely the same case.
    I think I agree with this.

    (I'm not entirely sure why, but my gut says yes).

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